Actually Retro just had an off and states that the sliders definatly prevented damage. Just think about it, with sliders your bike slides down the road on them, if you didn't have them some part of your bike would be in contact with the road.
He had both the frame and bar ends, and I'm thinking that BOTH are required in order to best protect your bike.
Not to mention decent, solid-mounted rearsets (check out Retro's pics in the thread below). I know for a fact that had I had sliders during my lowside in the canyons one year ago damage to the tank would have, if not completely prevented, severely minimized. I paid big $$ to fix an unnecessary amount of damage to my S4 so you could learn from my mistake/ neglect. Do get the sliders.
It will complete depend on the mishap. But its safe to say you will be better off with the sliders then without. Solid pegs are really a hug help also like the others said. But nothing will be a sure thing when a person goes down.